1. Field of the Invention
The present invention relates to iron-base sintered alloy for friction materials, useful as brakes for vehicles.
2. Description of Prior Art
Conventional sintered alloy friction materials used in brakes for rolling stock have better wear resistance than conventional cast iron brake blocks, but on the other hand, have a disadvantage that their friction coefficient is considered to be relatively high because of difficulties in incorporating lubricants functioning as free carbon in the cast iron brake blocks.
For the purpose of lowering the friction coefficient a lubricant is incorporated into the friction materials, and graphite or MoS.sub.2 is usually added to the sintered alloys for the purpose of improving the friction coefficient in a low-speed zone (low temperature zone) to which the brake material is subjected, but these lubricants produce only low lubricity at high temperatures, and in the worst case, not only the friction materials are burnt to the mating materials, thus unstabilizing the friction coefficient, but also the lubricants, when added excessive amounts, adhere to the tread surface of the wheels, thus causing the wheel slip.
In order to improve the friction coefficient at high temperatures, it has been tried to admix high-temperature lubricants for the high-speed zone, but these high-temperature lubricants, due to their high melting points, fail to exert satisfactory lubricating effect in the most frequently used intermediate zone between the low-speed zone and the high-speed zone.